The present invention relates to an ink set that is suitable in particular for an ink jet recording method, and the ink jet recording method.
In an ink jet recording method, recording is carried out by discharging a recording liquid from minute nozzles provided in a recording head through the vibration of piezoelectric elements, the action of thermal energy or the like; the method has advantages such as quietness during recording, it being possible to obtain high-resolution images at high speed by using a high-density head, and running costs being low. The method is thus used in various recording fields such as printers for personal computers, video printers, and graphics printers.
In the case of forming color images using the ink jet recording method, inks of at least the three primary colors magenta, yellow and cyan are used, and recording of full-color images is carried out by controlling the discharged amount and dot density of each of the inks and thus carrying out subtractive color mixing. In recent years, a method has become common in which, to obtain high-resolution images, for the magenta and cyan inks, dark and light inks having a different density to one another are used to reduce the sensation of graininess, whereby finer images can be obtained. It is important that each of the inks itself has excellent color reproducibility, and it is also important that good color reproducibility can be realized when printing is carried out combining the dark and light magenta ink, yellow ink and dark and light cyan ink to form red, green, blue and black.
Furthermore, water-based inks are mainly used as ink jet inks from a safety perspective with regard to odor, fire prevention and so on, and various characteristics are demanded of these inks, for example values of physical properties such as the viscosity and surface tension being insuitable ranges, nozzle clogging properties and storage stability being excellent, recorded images with high density (high optical density, vivid tones) being provided, and light-fastness and water resistance being excellent.
Most of these properties are satisfied by using a water-based ink having water or a mixed liquid of water and a water-soluble organic solvent as a main solvent, but color reproducibility, vividness, light-fastness and so on are greatly influenced by the colorant used, and hence various dyes have been investigated from hitherto. In answer to the above demands, in Japanese Patent Application Laid-open No. H5-214259, Japanese Patent Application Laid-open No. H8-310116, Japanese Patent Application Laid-open No. H9-3380, and Japanese Patent Application Laid-open No. H11-199809, it has been disclosed that excellent color reproducibility and light-fastness can be obtained even for secondary colors and tertiary colors through ink sets that use specific dye sets.
Moreover, the properties of magenta ink are poor with regard to light-fastness in particular, and hence in Japanese Patent Application Laid-open No. S57-5769, WO 96/24636, Japanese Patent Application Laid-open No. S62-192474, Japanese Patent Application Laid-open No. S63-19288, Japanese Patent Application Laid-open No. H10-306221, Japanese Patent Application Laid-open No. H1-29730, Japanese Patent Application Laid-open No. H11-158429, Japanese Patent Application Laid-open No. 2001-19881 and so on, magenta dye inks having excellent tone, vividness and light-fastness have been disclosed. Moreover, in Japanese Patent Application Laid-open No. H2-127482, a recording method has been disclosed using dark and light inks in which the type of dye differs between the dark ink and the light ink.
However, with printed articles produced through conventional inkjet recording using such dyes, there is a problem that the printed article fades upon exposure to light. Fading is particularly marked with a single magenta ink color, and as a result there is a problem that fading is also great with secondary and tertiary colors such as red, blue and composite black. Furthermore, it is still not possible to provide color printing with high resolution and fastness as a color recording method, for example storage reliability with regard to clogging properties, discharge stability and so on, and toning and color reproducibility are insufficient.
Moreover, in the above-mentioned recording method, reliability with regard to ink clogging and so on, tone, vividness and light-fastness may not be at a sufficiently satisfactory level, and even if light-fastness is excellent with a single color, when mixing with another color light fading is promoted through interaction with the other color, and as a result it is still not possible to provide excellent images in the case of full color image formation.
It is thus an object of the present invention to resolve these problems. That is, it is an object of the present invention to provide an ink set according to which light-fastness is excellent, storage stability with regard to clogging, discharge stability and so on is good, and tone, color reproducibility and other properties are satisfied, and a recording method using this ink set.
Moreover, it is an object of the present invention to provide a magenta ink according to which reliability with regard to clogging and soon is high, coloration in the case of a single color is excellent, vividness and light-fastness are obtained, and color images can be obtained that have excellent vividness and light-fastness even in mixed color parts were mixing is carried out with an ink of another color.
The above-mentioned objects are attained through the following invention.
An ink set of the present invention is an ink set that comprises inks each of which contains at least a dye, a water-soluble organic solvent and water, and that comprises a combination of magenta ink that contains a dye having a structure shown in general formula (I) below, yellow ink, and cyan ink. 
X: xe2x80x94COOM or xe2x80x94SO3M
Y: xe2x80x94H, xe2x80x94NH2 or xe2x80x94O(CH2)mH
M: xe2x80x94H, xe2x80x94Li, xe2x80x94Na, xe2x80x94K, xe2x80x94NH4 or xe2x80x94NH(CH2OH)3 
n=integer from 2 to 10
m=integer from 1 to 4
l=0 or 1
Moreover, in the ink set of the present invention, the yellow ink may be one that contains at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, and the cyan ink may be one that contains at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199.
Moreover, the magenta ink in the ink set of the present invention may be dark and light magenta ink comprising dark magenta ink containing a dye having a structure shown in general formula (I) above, and light magenta ink containing a dye having a structure shown general formula (II) below. 
(where Xxe2x80x2 indicates an anilino group substituted with at least one SO3M;
Yxe2x80x2 indicates OH, Cl or a morpholino group;
Mxe2x80x2 indicates H, Li, Na, K, ammonium, or an organic amine.)
Moreover, in the ink set of the present invention, the magenta ink may be dark and light magenta ink comprising dark magenta ink containing a dye having a structure shown in general formula (I) above, and light magenta ink containing a dye having a structure shown in general formula (II) above, the yellow ink may be one containing at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, and the cyan ink may be dark and light cyan ink containing at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199.
Furthermore, the present invention also relates to an ink jet recording method of forming a color image using at least dark and light magenta ink, yellow ink, and dark and light cyan ink, the ink jet recording method using the above-mentioned ink set.
By carrying out ink jet recording using an ink set according to the present invention, multi-color images can be provided having excellent storage stability, color reproducibility and other properties, with light-fastness being good not only for single colors but also secondary colors and tertiary colors. Following is a detailed description of the present invention, citing preferable embodiments of the present invention.
An ink set of the present invention is an ink set that comprises inks each of which contains at least a dye, a water-soluble organic solvent and water, and that comprises a combination of magenta ink that contains a dye having a structure shown in general formula (I) below, yellow ink, and cyan ink. 
X: xe2x80x94COOM or xe2x80x94SO3M
Y: xe2x80x94H, xe2x80x94NH2 or xe2x80x94O(CH2)mH
M: xe2x80x94H, xe2x80x94Li, xe2x80x94Na, xe2x80x94K, xe2x80x94NH4 or NH(CH2OH)3 
n=integer from 2 to 10
m=integer from 1 to 4
l=0 or 1
In the above ink set, the yellow ink may be one that contains at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, and the cyan ink may be one that contains at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199. By carrying out ink jet recording using this ink set, recorded image having high vividness and excellent light-fastness can be obtained.
The dye having a structure shown in general formula (I) above is preferably a water-soluble dye.
The following specific examples can be given of the dye represented by general formula (I) used in the magenta ink, but there is no limitation to these. 
It is preferable for the magenta ink to contain 1.0 to 4.0 wt % of the dye shown in above-mentioned general formula (I) relative to the total amount of the magenta ink, the yellow ink to contain 0.3 to 4.0 wt % of at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, relative to the total amount of the yellow ink, and the cyan ink to contain 1.0 to 4.0 wt % of at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199 relative to the total amount of the cyan ink. By making the dye contents be in these ranges, printing density and vividness, and reliability of the ink jet ink, for example ink clogging properties and discharge stability, can be secured.
Moreover, in the above ink set, the magenta ink may be dark and light magenta ink comprising dark magenta ink containing a dye having a structure shown in general formula (I) above, and light magenta ink containing a dye having a structure shown in general formula (II) below. 
(where Xxe2x80x2 indicates an anilino group substituted with at least one SO3M:
Yxe2x80x2 indicates OH, Cl or a morpholino group; and
Mxe2x80x2 indicates H, Li, Na, K, ammonium, or an organic amine.)
By carrying out ink jet recording using this ink set, recorded images having high vividness and excellent light-fastness can be obtained.
The magenta dyes shown in general formula (I) and general formula (II) above are preferably water-soluble dyes.
It is preferable for the dark magenta ink to contain 1 to 5 wt % of the dye having a structure shown in general formula (I) above relative to the total weight of the dark magenta ink, and for the light magenta ink to contain 0.5 to 4 wt % of the dye having a structure shown in general formula (II) above relative to the total weight of the light magenta ink.
The magenta dye represented by general formula (I) for the dark ink has extremely good vividness and light-fastness as a single color. Specific examples are the dyes shown as (M-1) to (M-12) above, but there is no limitation to these.
The dye concentration in the dark ink depends on the color value of the dye, but by making the ink contain the dye in an amount in a range of 1 to 5 wt %, sufficient coloring and density can be obtained. More suitably, the dye concentration is preferably such that the magenta OD value is 1.0 to 1.5 when solid printing (printing of completely filled-in blocks with 100% duty) is carried out on so-called normal paper, i.e. in a range of 1.5 to 3.5 wt %.
Moreover, the magenta dye represented by general formula (II) for the light ink has relatively good light-fastness as a single color, although not as good as that of the dye of general formula (I). When mixed with inks of other colors in particular, the magenta dye represented by general formula (II) has an action of not promoting light fading of other colors or white. Specific examples are the dyes shown below, but there is no limitation to these. 
The dye concentration in the light ink depends on the color value of the dye and the color balance when combined with the dark magenta ink, but by making the ink contain the dye in an amount in a range of 0.5 to 4 wt %, sufficient coloring and density can be obtained, and moreover the balance with the dark ink will be good. More suitably, the dye concentration is preferably such that the magenta OD value of the light ink is about 25% of the OD value of the dark magenta ink, i.e. in a range of 0.25 to 0.75, when solid printing (100% duty) is carried out on so-called normal paper, i.e. the dye concentration is preferably in a range of 1 to 3 wt %.
Moreover, in the above ink set, the magenta ink may be dark and light magenta ink comprising dark magenta ink containing a dye having a structure shown in general formula (I) above, and light magenta ink containing a dye having a structure shown in general formula (II) above, the yellow ink may be one containing at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, and the cyan ink may be dark and light cyan ink containing at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199. By carrying out ink jet recording using this ink set, recorded images having high vividness and excellent light-fastness can be obtained.
It is preferable for the dark magenta ink to contain 1.0 to 4.0 wt % of the dye shown in general formula (I) above relative to the total weight of the dark magenta ink, for the light magenta ink to contain 0.5 to 3.0 wt % of the dye shown in above-mentioned general formula (II) relative to the total weight of the light magenta ink, for the yellow ink to contain 0.3 to 4.0 wt % of at least one dye selected from the group consisting of a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, and a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, relative to the total weight of the yellow ink, and for the dark and light cyan ink to comprise dark cyan ink containing 1.0 to 4.0 wt % of at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199 relative to the total weight of the dark cyan ink, and light cyan ink containing 0.5 to 3.0 wt % of at least one dye selected from the group consisting of C.I. Direct Blue 86 and C.I. Direct Blue 199 relative to the total weight of the light cyan ink. By making the dye contents be in these ranges, printing density and vividness, and reliability of the inkjet ink, for example ink clogging properties and discharge stability, can be secured.
Specific examples of the dye represented by general formula (I) used in the dark magenta ink are previously mentioned (M-1) to (M-12), but there is no limitation to these.
Specific examples of the dye represented by general formula (II) used in the light magenta ink are previously mentioned (LM-1) to (LM-12), but there is no limitation to these.
In addition to the specific dyes described above, the magenta ink, yellow ink and cyan ink described above also each contains water or a mixed liquid of water and a water-soluble organic solvent. The water is preferably deionized water rather than general water, which contains a variety of ions, and the water-soluble organic solvent is preferably a solvent having low volatility from the viewpoint of suppressing clogging. Examples include polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, 1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol and glycerol, glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether, nitrogen-containing solvents such as formamide, dimethylformamide, diethanolamine, triethanolamine, 1,3-dimethyl-2-imidazolidinone, 2-pyrrolidone and N-methyl-2-pyrrolidone, and sulfur-containing solvents such as thiodiglycol and dimethylsulfoxide. However, there is no limitation to these compounds in the present invention, and it is also acceptable to include a plurality of types of water-soluble organic solvent. Moreover, these solvents may be used singly, or two or more types may be used together. It is suitable for an ink jet ink for the content of the water-soluble organic solvent(s) to be in a range of 3.0 to 50.0 wt % relative to the total weight of the ink. By making the content be at least 3.0 wt %, clogging at the nozzle tips becomes not prone to occur, and by making the content be not more than 50.0 wt %, the occurrence of phenomena such as dropping of the drying ability of recorded images and smudging of images leading to a drop in printing quality can be prevented.
Furthermore, to prevent ink clogging, a wetting agent that is a solid at normal temperatures and has a moisture-absorbing ability such as urea, trimethylol ethane or trimethylol propane is also effective; the amount added thereof is preferably 2 to 20 wt %, more preferably 5 to 10 wt %, relative to the total weight of the ink.
Moreover, dropping of the printing quality, smudging and the like are problems, but by including a glycol ether or the like or an acetylenic glycol type nonionic surfactant, these problems can be resolved, and vivid images with no smudging can be obtained. More preferably, by using a glycol ether or the like and an acetylenic glycol type nonionic surfactant together, color images with yet better vividness and printing quality can be obtained.
A water-soluble organic solvent as mentioned earlier is preferable as the glycol ether, with particularly preferable examples being diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether and dipropylene glycol monobutyl ether. The amount added may be the same as that of the water-soluble organic solvent mentioned earlier, but is more preferably selected from a range of 3.0 to 20.0 wt %. If it is less than 3.0 wt % then effects will hardly be obtained, and if it is more than 20.0 wt % then smudging will actually become greater, the image as a whole will become blurred, and the printing quality will be reduced; it is thus preferable to use the glycol ether in the mentioned range.
Examples of the acetylenic glycol type nonionic surfactant include Olfine E1010, Olfine STG and Olfine 104E (all made by Nissin Chemical Industry Co., Ltd.). The amount added thereof is preferably in a range of 0.01 to 3.0 wt % relative to the total weight of the ink.
The water content depends on the type and composition of the above-mentioned solvent component and the desired properties of the recording liquid and can be determined from a broad range, being in a range from 10.0 to 70.0 wt % of the total weight of the ink.
In addition to the above-mentioned components, as necessary additives can be mixed into the ink of the present invention for giving the ink desired properties, for example viscosity regulators such as sodium alginate and polyvinyl alcohol, pH regulating agents such as alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide and pH buffering agents such as ammonium phosphate, preservatives, corrosion-preventing agents, antioxidants, fungicides, and chelating agents.
Furthermore, to promote drying of the ink after image formation, it is preferable for the ink compositions of the present invention to contain lower alcohols such as ethanol, 1-propanol and 2-propanol, anionic surfactants such as fatty acid salts and alkyl sulfate ester salts, and nonionic surfactants such as acetylenic glycols, polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters. The lower alcohol content is preferably in a range of 2 to 10 wt %, more preferably 2 to 6 wt %, relative to the total amount of the ink, and the surfactant content is preferably in a range of 0.01 to 2 wt % relative to the total amount of the ink. If these contents are less than this, then the effect of promoting drying will not be sufficient, whereas if they are greater than this, then smudging may occur, there will be adverse effects on the state of discharge (or flying) of the ink with the ink jet recording method, and the image quality will drop.
Furthermore, water-soluble polymers or water-soluble resins, antifoaming agents, pH regulators, fungicides and the like may be included in the ink of the present invention as necessary.
According to the ink jet recording method of the present invention, color reproducibility is excellent for each of magenta, yellow and cyan, and in addition good light-fastness can be obtained both for single colors and for secondary colors and tertiary colors.
Moreover, the inkjet recording method of the present invention is a method of carrying out recording using the ink described above, but any conventional publicly-known method can be used as the head discharge method; in particular, in the case of a method in which droplets are discharged by using the vibrations of piezoelectric elements or a method using thermal energy, an excellent ink jet recording method can be carried out.
Regarding the manufacture of the ink described above, manufacturing can be carried out following normal methods. An example is a method in which the ink is prepared by thoroughly mixing and dissolving the various components, carrying out pressure filtration using a membrane filter of pore size 0.8 xcexcm, and then carrying out deaeration treatment using a vacuum pump.
Then, the ink and ink set according to the present invention can be used with various recording methods. Examples of recording methods using the ink and ink set are an ink jet recording method, a recording method using a writing instrument such as a pen, and other types of printing method using a recorder, a pen plotter or the like. In particular, the ink and ink set according to the present invention can be used especially suitably with an ink jet recording method in which recording is carried out by discharging a recording liquid from minute nozzles provided in a recording head.
Any conventional publicly-known method can be used as the ink jet recording method; in particular, in the case of a method in which droplets are discharged using the vibrations of piezoelectric elements or a method using thermal energy, excellent image recording can be carried out.